Light control device and light control method

ABSTRACT

A light control device  1  includes a light source  10 , a prism  20 , a spatial light modulator  30 , a drive unit  31 , a control unit  32 , a lens  41 , an aperture  42 , and a lens  43 . The spatial light modulator  30  is a phase modulating spatial light modulator, includes a plurality of two-dimensionally arrayed pixels, is capable of phase modulation in each of these pixels in a range of 4π, and presents a phase pattern to modulate the phase of light in each of the pixels. This phase pattern is produced by superimposing a blazed grating pattern for light diffraction with a phase modulation range of 2π or less and a phase pattern having a predetermined phase modulation distribution with a phase modulation range of 2π or less.

TECHNICAL FIELD

The present invention relates to a light control device and a lightcontrol method.

BACKGROUND ART

Spatial light modulators can modulate the intensity or phase of inputlight in each of a plurality of two-dimensionally arrayed pixels. Suchspatial light modulators include an intensity modulation type spatiallight modulator that can modulate only the intensity, a phase modulationtype spatial light modulator that can modulate only the phase, and anintensity and phase modulation type spatial light modulator that canmodulate both of the intensity and phase. Light output after beingmodulated in intensity or phase in each pixel of the spatial lightmodulator, as a result of, for example, being condensed by a condensingoptical system provided at a subsequent stage of the spatial lightmodulator, can process an object existing at its condensing position.

The intensity modulating spatial light modulator adjusts thetransmittance of input light pixel by pixel, and cannot use light of apart that has not been transmitted therethrough, and is thus inferior inlight utilization efficiency. It is not easy for the intensity and phasemodulating spatial light modulator to control intensity modulation andphase modulation in each pixel independently of each other, and handlingthereof is difficult.

On the other hand, the phase modulating spatial light modulatormodulates the phase of input light pixel by pixel, and can output almostentire light, and is thus excellent in light utilization efficiency.Moreover, the phase modulating spatial light modulator, as a result ofpresenting a phase pattern prepared from a computer-generated hologramor the like, has a high degree of freedom in the phase distribution in abeam section of output light, and has a high degree of freedom in thecondensing position of output light by the condensing optical system. Asan application of light control using such a phase modulating spatiallight modulator, processing of the surface and interior of a processingobject, generation of a Laguerre-Gaussian mode beam, and the like can bementioned.

Moreover, it has been known that the intensity of outputting light thatis phase-modulated pixel by pixel in the phase modulating spatial lightmodulator can be modulated (refer to Non-Patent Literature 1). This isfor causing the phase modulating spatial light modulator to present aphase pattern produced by superimposing a blazed grating pattern forlight diffraction and a phase pattern having a predetermined phasemodulation distribution, and adjusting the light diffraction efficiencyin the spatial light modulator by adjusting the blazed grating pattern.Accordingly, it has been considered that light that is output afterbeing diffracted by the spatial light modulator can have a desiredintensity distribution and phase distribution in its beam section.

Moreover, it has been considered that, generally, since the phase α of alight wave is equivalent to a phase (α+2nπ), it is sufficient thatoptical phase modulation in each pixel of the spatial light modulator ispossible in a range of 2π. Here, n is an arbitrary integer. For example,when the phase modulation amount exceeds 2π, it suffices to add orsubtract 2nπ with respect to the phase modulation amount (hereinafter,referred to as “phase folding”) to thereby make the phase modulationamount a value within a range from 0 to 2π. It has been considered that,even if the phase modulation amount after phase folding is thus providedas the phase modulation amount of each pixel of the spatial lightmodulator, no problem arises in principle.

Conventional spatial light modulators are set so as to have a phasemodulation range of 2π. This is because, if the phase modulation rangein the spatial light modulator is 2π, a phase modulation exceeding 2πcan also be expressed in principle by performing phase folding in thephase pattern. Moreover, this is because a spatial light modulatorhaving a phase modulation range exceeding 2π is not only redundant, butalso causes a reduction in resolution and a reduction in response speedin terms of the relationship between the input gradation value and phasemodulation amount.

CITATION LIST Non Patent Literature

-   Non-Patent Literature 1: Joseph P. Kirk and Alan L. Jones,    “Phase-only complex-valued spatial filter,” Journal of the optical    society of America, Vol. 61, No. 8, 1971

SUMMARY OF INVENTION Technical Problem

Meanwhile, the present inventor has been engaged in various research anddevelopment, taking advantage of being able to cause a phase modulatingspatial light modulator to present a phase pattern produced bysuperimposing a blazed grating pattern and a predetermined phasepattern, and to modulate the intensity of outputting light that isphase-modulated pixel by pixel in this spatial light modulator. Thepresent inventor, in the course of research and development, hasdiscovered that a phenomenon of the intensity distribution and the phasedistribution in a beam section of light output from the spatial lightmodulator different from the desired effect may occur, that is, aphenomenon resulting in degradation in beam quality of light output fromthe spatial light modulator may occur. Further, the present inventor hasdiscovered that the phenomenon is due to phase folding.

The present invention has been made in order to solve the aboveproblems, and it is an object of the present invention to provide alight control device and light control method capable of obtaining lighthaving a desired beam section in the technique of causing a phasemodulating spatial light modulator to present a phase pattern producedby superimposing a blazed grating pattern and a phase pattern having apredetermined phase modulation distribution.

Solution to Problem

A light control device according to the present invention includes (1) alight source that outputs light, (2) a phase modulating spatial lightmodulator that is capable of phase modulation in each of a plurality oftwo-dimensionally arrayed pixels in a range of 4π, is input with lightoutput from the light source, presents a phase pattern to modulate thephase of light in each of the pixels, and outputs light after beingphase-modulated by this phase pattern, and (3) a control unit thatcauses the spatial light modulator to present a phase pattern producedby superimposing a blazed grating pattern for light diffraction with aphase modulation range of 2π or less and a phase pattern having apredetermined phase modulation distribution with a phase modulationrange of 2π or less, and adjusts the light diffraction efficiency in thespatial light modulator by adjusting the blazed grating pattern.

In the light control device according to the present invention, it ispreferable that the control unit causes the spatial light modulator topresent a phase pattern for which the blazed grating pattern having alight diffraction efficiency distribution according to an intensitydistribution in a beam section of a Laguerre-Gaussian mode beam with aspecific index and the phase pattern having a phase modulationdistribution according to a phase distribution in a beam section of theLaguerre-Gaussian mode beam are superimposed.

Moreover, in the light control device according to the presentinvention, it is preferable that the control unit causes the spatiallight modulator to present a phase pattern for which the blazed gratingpattern having a light diffraction efficiency distribution according toan intensity distribution of light having a specific intensitydistribution and phase distribution in a beam section and the phasepattern having a phase modulation distribution according to the phasedistribution are superimposed.

A light control method according to the present invention uses (1) alight source that outputs light, and (2) a phase modulating spatiallight modulator that is capable of phase modulation in each of aplurality of two-dimensionally arrayed pixels in a range of 4π, is inputwith light output from the light source, presents a phase pattern tomodulate the phase of light in each of the pixels, and outputs lightafter being phase-modulated by this phase pattern, and (3) causes thespatial light modulator to present a phase pattern produced bysuperimposing a blazed grating pattern for light diffraction with aphase modulation range of 2π or less and a phase pattern having apredetermined phase modulation distribution with a phase modulationrange of 2π or less, and adjusts the light diffraction efficiency in thespatial light modulator by adjusting the blazed grating pattern.

It is preferable that the light control method according to the presentinvention causes the spatial light modulator to present a phase patternfor which the blazed grating pattern having a light diffractionefficiency distribution according to an intensity distribution in a beamsection of a Laguerre-Gaussian mode beam with a specific index and thephase pattern having a phase modulation distribution according to aphase distribution in a beam section of the Laguerre-Gaussian mode beamare superimposed.

It is preferable that the light control method according to the presentinvention causes the spatial light modulator to present a phase patternfor which the blazed grating pattern having a light diffractionefficiency distribution according to an intensity distribution of lighthaving a specific intensity distribution and phase distribution in abeam section and the phase pattern having a phase modulationdistribution according to the phase distribution are superimposed.

Advantageous Effects of Invention

According to the present invention, light having a desired beam sectioncan be obtained in the technique of causing a phase modulating spatiallight modulator to present a phase pattern produced by superimposing ablazed grating pattern and a phase pattern having a predetermined phasemodulation distribution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a light control device 1.

FIG. 2 is a view showing a blazed grating pattern.

FIG. 3 is a chart showing an example of the phase modulationdistribution in a blazed grating pattern.

FIG. 4 is a graph showing a relationship between the k-value anddiffraction efficiency in a blazed grating pattern presented in anactual spatial light modulator.

FIG. 5 is a chart showing an example of the phase modulationdistribution in a blazed grating pattern.

FIG. 6 is a table showing an example of the phase modulation amount ofeach pixel in the blazed grating pattern.

FIG. 7 is a chart showing an example of the phase modulationdistribution in a phase pattern.

FIG. 8 is a chart showing a phase modulation distribution in a phasepattern where the blazed grating pattern (FIG. 5 and FIG. 6) and thephase pattern having a predetermined phase modulation distribution (FIG.7) are superimposed.

FIG. 9 is a chart showing a phase modulation distribution in a phasepattern after performing phase folding for the phase pattern φ_(result)(FIG. 8).

FIG. 10 is a view showing an example of the intensity distribution in abeam section of light output from a spatial light modulator in the caseof a comparative example.

FIG. 11 is a view showing an intensity distribution in a beam section ofan LG_(1,3) light.

FIG. 12 is a view showing a blazed grating pattern φ_(grating) to obtainthe intensity distribution (FIG. 11) in a beam section of an LG_(1,3)light.

FIG. 13 is a view showing a desired phase pattern φ_(desire) to obtain aphase distribution in a beam section of an LG_(1,3) light.

FIG. 14 is a view showing an intensity distribution in a beam section ofan LG_(1,3) light generated by the present embodiment.

FIG. 15 is a view showing an intensity distribution in a beam section ofan LG_(1,3) light generated by the comparative example.

FIG. 16 is a chart showing examples of the intensity distribution beforebeam shaping and the intensity distribution after beam shaping.

REFERENCE SIGNS LIST

1 . . . light control device, 2 . . . imaging device, 10 . . . lightsource, 20 . . . prism, 30 . . . spatial light modulator, 31 . . . driveunit, 32 . . . control unit, 41 . . . lens, 42 . . . aperture, 43 . . .lens.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the best mode for carrying out the present invention willbe described in detail with reference to the accompanying drawings.Also, the same components are denoted with the same reference numeralsin the description of the drawings, and overlapping description will beomitted.

FIG. 1 is a configuration diagram of a light control device 1. The lightcontrol device 1 shown in this figure includes a light source 10, aprism 20, a spatial light modulator 30, a drive unit 31, a control unit32, a lens 41, an aperture 42, and a lens 43. Also, in this figure, notonly the light control device 1 but also an imaging device 2 is shown.

The phase modulating spatial light modulator to be used in the presentinvention may be either a reflection type or a transmission type. Thereflective spatial light modulator may be any of the LCOS (LiquidCrystal on Silicon) type, the MEMS (Micro Electro Mechanical Systems)type, and the optical address type. Moreover, the transmissive spatiallight modulator may be an LCD (Liquid Crystal Display) or the like. InFIG. 1, a reflective spatial light modulator is shown as the spatiallight modulator 30.

The light source 10 is for outputting light that is required to bephase-modulated by the spatial light modulator 30, is preferably a laserlight source, may be a pulsed laser light source such as a femtosecondlaser light source and a Nd:YAG laser light source, and may be a CWlaser light source such as a He—Ne laser light source. It is preferablethat light output from the light source 10 is collimated by a collimatorlens after passing through a spatial filter.

The prism 20 has a first reflecting surface 21 and a second reflectingsurface 22. The first reflecting surface 21 of the prism 20 is inputwith light output from the light source 10, and reflects the lighttoward the spatial light modulator 30. The second reflecting surface 22of the prism 20 is input with light output from the spatial lightmodulator 30, and reflects the light toward the lens 41.

The spatial light modulator 30 is a phase modulating spatial lightmodulator, includes a plurality of two-dimensionally arrayed pixels, iscapable of phase modulation in each of these pixels in a range of 4π,and can present a phase pattern to modulate the phase of light in eachof the pixels. The spatial light modulator 30 is input with light thathas reached after being output from the light source 10 and reflected onthe first reflecting surface 21 of the prism 20, and outputs the lightafter being phase-modulated by the phase pattern to the secondreflecting surface 22 of the prism 20. Examples of the phase pattern tobe presented in the spatial light modulator 30 that can be mentionedinclude a CGH (Computer-Generated Hologram) determined by numericalcalculation.

The drive unit 31 is for setting the phase modulation amount in each ofthe two-dimensionally arrayed pixels of the spatial light modulator 30,and provides a signal for the pixel-by-pixel setting of the phasemodulation amount to the spatial light modulator 30. The drive unit 31sets the phase modulation amount in each of the two-dimensionallyarrayed pixels of the spatial light modulator 30 to thereby cause thespatial light modulator 30 to present a phase pattern.

The control unit 32 is formed of, for example, a computer, and controlsoperation of the drive unit 31 to thereby cause a phase pattern to bewritten into the spatial light modulator 30 from the drive unit 31. Thatis, the control unit 32 stores a phase pattern A that is required to bepresented by the spatial light modulator 30, or prepares that phasepattern A, and causes the phase pattern A to be written into the spatiallight modulator 30 from the drive unit 31.

This phase pattern A is produced by superimposing a blazed gratingpattern for light diffraction with a phase modulation range of 2π orless and a phase pattern having a predetermined phase modulationdistribution with a phase modulation range of 2π or less. This phasepattern having a predetermined phase modulation distribution preferablyincludes a component to realize a desired phase distribution in a lightbeam section, and also further includes a component to correct a phasedistortion of an optical system including the spatial light modulator 30in the light control device 1. The light diffraction efficiency in thespatial light modulator 30 can be adjusted by adjusting the blazedgrating pattern.

The lens 41 is input with light output from the spatial light modulator30 and reflected on the second reflecting surface 22 of the prism 20.The lens 41 and the lens 43 form a 4f optical system, and has an openingof the aperture 42 disposed at a focal position therebetween. Theaperture 42 is disposed so that only diffracted light of a desired orderpasses therethrough.

The imaging device 2 receives light B output from the lens 43 of thelight control device 1, and obtains an intensity distribution in a beamsection of the light B. The imaging device 2 is for observing thequality of light output from the light control device 1. Also, in thecase of use for processing or the like, a new lens is disposed at asubsequent stage of the lens 43, and a processing object is disposed atits condensing position.

The general operation of the light control device 1 is as follows. Bythe drive unit 31 controlled by the control section 32, a phase patternproduced by superimposing a blazed grating pattern and a phase patternis presented in the spatial light modulator 30. The light output fromthe light source 10 is reflected on the first reflecting surface 21 ofthe prism 20, and input to the spatial light modulator 30.

The light input to the spatial light modulator 30 is output after beingdiffracted by the blazed grating pattern out of the phase patternpresented in the spatial light modulator 30. The diffraction efficiencyat that light diffraction varies depending on the shape of the blazedgrating pattern, and may vary depending on the position on a lightincident surface of the spatial light modulator 30. Moreover, the lightdiffracted and output from the spatial light modulator 30 has beenphase-modulated by the phase pattern having a predetermined phasemodulation distribution out of the phase pattern presented in thespatial light modulator 30.

The light output from the spatial light modulator 30 is reflected on thesecond reflecting surface 22 of the prism 20, passes through the lens41, the aperture 42, and the lens 43, and received by the imaging device2 to obtain an intensity distribution in a light beam section. At thistime, the lens 41, the aperture 42, and the lens 43 are formed in aconfiguration to allow diffracted light of a desired diffraction orderout of the light output from the spatial light modulator 30 toselectively pass therethrough. Therefore, the light B to be output tothe imaging device 2 from the lens 43 is a light having a desiredintensity distribution and phase distribution.

Next, the phase pattern to be presented in the spatial light modulator30 will be described in detail. This phase pattern is produced bysuperimposing a blazed grating pattern for light diffraction and a phasepattern having a predetermined phase modulation distribution. FIG. 2 isa view showing a blazed grating pattern. In this figure, the phasemodulation amount (modulation width of 2π) of each pixel is shown bygrayscale. When light is input to the spatial light modulator 30 wheresuch a blazed grating pattern is presented, the light is diffracted. Thediffraction efficiency at that light diffraction varies depending on theshape of the blazed grating pattern.

A blazed grating pattern φ_(grating) having N pixels along a specificdirection on the light incident surface of the spatial light modulator30 as one period is expressed by the following formula (1). Here, ndenotes a pixel position within the period along the specific direction.k can take a value not less than 0 and not more than 1. Therefore, theblazed grating pattern φ_(grating) has a phase modulation range of 2kπ,which is 2π or less.

$\begin{matrix}\left\lbrack {{Numerical}\mspace{14mu}{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{{\phi_{grating}(n)} = {2{\pi \cdot k}\frac{n - {N/2}}{N}}} & (1)\end{matrix}$

The theoretical diffraction efficiency I_(+1th) of this blazed gratingpattern φ_(grating) is expressed by the following formula (2), andvaries depending on the k-value. Where k takes a value of 1, thetheoretical diffraction efficiency I_(+1th) has the maximum value of 1.

$\begin{matrix}\left\lbrack {{Numerical}\mspace{14mu}{Formula}\mspace{14mu} 2} \right\rbrack & \; \\{I_{{+ 1}{th}} = \frac{\sin\left( {\pi\left( {1 - k} \right)} \right)}{\pi\left( {1 - k} \right)}} & (2)\end{matrix}$

Therefore, if the k-values are uneven and distributed in the lightincident surface of the spatial light modulator 30, the lightdiffraction efficiency in the light incident surface of the spatiallight modulator 30 is also distributed. FIG. 3 is a chart showing anexample of the phase modulation distribution in a blazed grating patternφ_(grating). In this figure, the horizontal axis indicates the pixelposition. As in the example shown in this figure, when the k-valuebecomes larger as it moves to the right, the diffraction efficiencybecomes higher as it moves to the right. FIG. 4 is a graph showing arelationship between the k-value and diffraction efficiency in a blazedgrating pattern φ_(grating) presented in an actual spatial lightmodulator. As shown in this figure, the larger the k-value, the higherthe diffraction efficiency. In addition, the angle of diffraction doesnot depend on the k-value.

A phase pattern φ_(result) to be presented in the spatial lightmodulator 30 is a pattern for which the blazed grating patternφ_(grating) as described above and a desired phase pattern φ_(desire)serving as a phase pattern are superimposed, and is expressed by thefollowing formula (3). Alternatively, a phase pattern φ_(result) to bepresented in the spatial light modulator 30 is produced by superimposingthe blazed grating pattern φ_(grating) as described above, a desiredphase pattern φ_(desire) serving as a phase pattern, and a distortioncorrection pattern φ_(correction), and expressed by the followingformula (4).[Numerical Formula 3]φ_(result)=φ_(grating)+φ_(desire)  (3)[Numerical Formula 4]φ_(result)=φ_(grating)+φ_(desire)+φ_(correction)  (4)

The desired phase pattern φ_(desire) is a pattern to realize a desiredphase distribution in a light beam section, and its phase modulationrange is 2π or less. Moreover, the distortion correction patternφ_(correction) is a pattern to correct a phase distortion of the opticalsystem in the light control device 1, and the phase modulation range isgenerally on the order of a few π. The phase distortion of the opticalsystem in the light control device 1 can exist in the first reflectingsurface 21 and the second reflecting surface 22 of the prism 20, thespatial light modulator 30, and the lenses 41 and 43. The lightdiffracted and output from the spatial light modulator 30 where such aphase pattern φ_(result) is presented has a desired intensitydistribution and phase distribution in its beam section.

In the following, for simplification of description, the above-describedformula (3) and formula (4) will be expressed by the following formula(5). A phase pattern φ_(phase) in this formula (5) is the desired phasepattern φ_(desire) in the formula (3), or is alternatively a sum of thedesired phase pattern φ_(desire) and the distortion correction patternφ_(correction) in the formula (4).[Numerical Formula 5]φ_(result)=φ_(grating)+φ_(phase)  (5)

Particularly, in the present embodiment, by the following formula (6),phase folding is performed for a phase pattern φ_(phase), and the phasepattern φ_(phase) after phase folding is superimposed on the blazedgrating pattern φ_(grating) to provide this as the phase patternφ_(result) to be presented in the spatial light modulator 30. The phasepattern φ_(phase) after phase folding has a phase modulation range of 2πor less.[Numerical Formula 6]φ_(phase)=mod(φ_(phase),2π)  (6)

The phase pattern φ_(result) to be presented in the spatial lightmodulator 30 has a phase modulation range of 4π or less in the presentembodiment. As an example of the blazed grating pattern φ_(grating)included in this phase pattern φ_(result), one shown in FIG. 5 and FIG.6 is considered. FIG. 5 is a chart showing an example of the phasemodulation distribution in a blazed grating pattern. In this figure, thehorizontal axis indicates the pixel position. Moreover, FIG. 6 is atable showing an example of the phase modulation amount of each pixel inthe blazed grating pattern. In this blazed grating pattern φ_(grating),the k-value is 0.5, the N-value is 8, and the difference in the phasemodulation amount between two adjacent pixels is 0.125π. In FIG. 5, theblazed grating pattern φ_(grating) for approximately six periods isshown.

As an example of the phase pattern φ_(phase) included in the phasepattern φ_(result), one shown in FIG. 7 is considered. FIG. 7 is a chartshowing an example of the phase modulation distribution in a phasepattern. In this figure, the horizontal axis indicates the pixelposition. This phase pattern φ_(phase), as a result of phase folding of2π performed according to necessity, includes a part where the phasemodulation amount is 0 and a part where the phase modulation amount is1.25π.

FIG. 8 is a chart showing a phase modulation distribution in a phasepattern φ_(result) where the blazed grating pattern φ_(grating) (FIG. 5and FIG. 6) and the phase pattern φ_(phase) (FIG. 7) are superimposed.In this figure, the horizontal axis indicates the pixel position. In thephase pattern φ_(result) shown in this figure, the phase modulationamount is 2π or more.

FIG. 9 is a chart showing a phase modulation distribution in a phasepattern after performing phase folding by 2π for the phase patternφ_(result) (FIG. 8). In this figure as well, the horizontal axisindicates the pixel position. In the phase modulation distribution inthe phase pattern (FIG. 9) after phase folding, 2π has been subtractedfrom the phase modulation amounts for pixels with phase modulationamounts exceeding 2π in the phase pattern φ_(result) (FIG. 8) beforephase folding, and the phase modulation amount in each pixel is in arange from 0 to 2π.

In the case of the present embodiment where the spatial light modulator30 having a phase modulation range of 4π is used, the phase pattern(FIG. 8) before phase folding (4π or less) is presented in that spatiallight modulator 30. On the other hand, in the case of a comparativeexample where a spatial light modulator having a phase modulation rangeof 2π is used, the phase pattern (FIG. 9) after phase folding ispresented in that spatial light modulator.

The phase pattern (FIG. 8) before phase folding and the phase pattern(FIG. 9) after phase folding have mutually equivalent effects inprinciple. However, in an actual spatial light modulator, a regioncalled a flyback region where the phase is rounded to cause an incorrectdisplay exists in a part where the difference in the phase modulationamount between two adjacent pixels is large. That is, as compared to thephase pattern (FIG. 8) before phase folding, in the phase pattern (FIG.9) after phase folding, the flyback regions exist at the positions shownby the arrows in the figure, and accordingly, light having a desiredintensity distribution and phase distribution cannot be obtained.

In the case of a comparative example where the phase pattern (FIG. 9)after phase folding is presented in the spatial light modulator having aphase modulation range of 2π, the difference in the phase modulationamount between two adjacent pixels that has been slight before phasefolding becomes approximately 2π after phase folding. When an actualspatial light modulator is made to present such a phase pattern afterphase folding, in a part where the difference in the phase modulationamount is large between two adjacent pixels in that spatial lightmodulator, the phase modulation amount cannot completely sharply change,and crosstalk occurs between the two adjacent pixels. Such a part(flyback region) where crosstalk exists is considered to have aparticularly remarkable effect when there is a step of approximately 2πin the phase modulation amount between the two adjacent pixels and theflyback region exists within the periodic structure of a blazed gratingpattern.

In the case where a change in the phase modulation amount in the phasepattern to be presented in the spatial light modulator is relativelymoderate, there are few flyback regions, and the effect that the flybackregions have on the intensity distribution and phase distribution in abeam section of a light output from the spatial light modulator can bemostly disregarded.

FIG. 10 is a view showing the intensity distribution in a beam sectionof light output from a spatial light modulator as another example of thecomparative example. This is a result obtained by displaying in thespatial light modulator 30 a pattern for which a blazed grating patternφ_(grating), a desired phase pattern φ_(desire), and a distortioncorrection pattern φ_(correction) are superimposed, and phase folding isapplied by 2π. A spatial light modulator having a phase modulationamount of 2π is used here. Moreover, the desired phase patternφ_(desire) is with the intention that the intensity distribution in abeam section of light output from the spatial light modulator becomesuniform. In the intended intensity distribution in a beam section oflight, the black region in the figure is to extend over the whole areaentirely. However, in the actually obtained intensity distribution in abeam section of light, regions with a strong intensity (white regions inthe figure) exist against the intention described above. This isbecause, besides the blazed grating pattern φ_(grating) having manyflyback regions, the phase pattern φ_(result) produced by superimposingthereon the desired phase pattern φ_(desire) and the distortioncorrection pattern φ_(correction) has still more flyback regions.

In the comparative example, a part where a failure has been actuallyfound in a beam section of output light is coincident with a place wherethe phase modulation amount sharply changes in the phase pattern. In anactual spatial light modulator, degradation in the quality of outputlight becomes a problem that cannot be disregarded. Thus, in thecomparative example, light having a desired intensity distribution andphase distribution cannot be obtained due to the effect of flybackregions.

On the other hand, in the present embodiment, a phase pattern (forexample, FIG. 8) with a phase modulation range of 4π or less ispresented in the spatial light modulator 30 having a phase modulationrange of 4π in each pixel. Therefore, light having a desired intensitydistribution and phase distribution can be obtained in a beam section,without the necessity for performing phase folding.

Next, description will be given of the case where a Laguerre-Gaussianmode beam is generated by use of the light control device 1 according tothe present embodiment. The Laguerre-Gaussian mode beam has an intensitydistribution and phase distribution to be specified by a radial indexand an azimuthal index in its beam section. In the following,description will be given of the case where a Laguerre-Gaussian modebeam with a radial index of 1 and an azimuthal index of 3 (hereinafter,described as an “LG_(1,3) light”) is generated.

FIG. 11 is a view showing an intensity distribution in a beam section ofan LG_(1,3) light. A blazed grating pattern φ_(grating) is set so thatthe intensity distribution in a beam section becomes such a distributionas shown in the same figure. FIG. 12 is a view showing a blazed gratingpattern φ_(grating) to obtain the intensity distribution (FIG. 11) in abeam section of an LG_(1,3) light. Moreover, FIG. 13 is a view showing adesired phase pattern φ_(desire) to obtain a phase distribution in abeam section of an LG_(1,3) light. In each of FIG. 12 and FIG. 13, thephase modulation amount of each pixel is shown by grayscale.

A phase pattern φ_(result) for generating an LG_(1,3) light by thespatial light modulator 30 is a pattern for which the above-describedblazed grating pattern φ_(grating) and desired phase pattern φ_(desire)are superimposed, and a distortion correction pattern φ_(correction) isfurther superimposed thereon. However, a phase pattern φ_(phase) being asum of the desired phase pattern φ_(desire) and the distortioncorrection pattern φ_(correction) is applied with phase folding, and hasa phase modulation range of 2π or less. This phase pattern φ_(result) ispresented in the spatial light modulator 30.

In the present embodiment, since a phase pattern φ_(result) produced bysuperimposing a blazed grating pattern φ_(grating) for light diffractionwith a phase modulation range of 2π or less and a phase patternφ_(phase) having a predetermined phase modulation distribution with aphase modulation range of 2π or less is presented in the spatial lightmodulator 30 with a phase modulation range of 4π, an LG_(1,3) lighthaving a desired intensity distribution and phase distribution can beobtained, without the necessity for performing phase folding for thephase pattern φ_(result). On the other hand, in the comparative example,since a spatial light modulator with a phase modulation range of 2π isused, a phase pattern after phase folding is displayed in that spatiallight modulator, and therefore, an LG_(1,3) light having a desiredintensity distribution and phase distribution cannot be obtained.

FIG. 14 is a view showing an intensity distribution in a beam section ofan LG_(1,3) light generated by the present embodiment. Moreover, FIG. 15is a view showing an intensity distribution in a beam section of anLG_(1,3) light generated by the comparative example. As can beunderstood by comparing both, the LG_(1,3) light generated by thepresent embodiment has an intensity distribution close to a desired onein comparison with the LG_(1,3) light generated by the comparativeexample.

A Laguerre-Gaussian mode beam to be thus generated by the light controldevice 1 according to the present embodiment is close to a desired onein terms of not only the phase distribution but also the intensitydistribution in a beam section, and has high mode purity. Therefore,this Laguerre-Gaussian mode beam can be preferably used in opticaltweezers or a quantum operation.

Next, description will be given of beam shaping using the light controldevice 1 according to the present embodiment. Beam shaping is atechnique for converting an input light where the intensity distributionin a beam section is non-uniform to an output light where the intensitydistribution in a beam section is as desired. FIG. 16 is a chart showingexamples of the intensity distribution before beam shaping and theintensity distribution after beam shaping. The solid line shows theintensity distribution before beam shaping, while the broken line showsthe intensity distribution after beam shaping. It is provided that thecloser to the center of the intensity distribution (solid line) beforebeam shaping, the stronger the intensity, and the intensity distribution(broken line) after beam shaping is uniform.

For a blazed grating pattern φ_(grating) to be used for this beamshaping, the distribution of k-values is set so as to have a diffractionefficiency distribution according to a ratio of the intensitydistribution before beam shaping and the intensity distribution afterbeam shaping in a beam section. Moreover, a phase pattern φ_(result) tobe presented in the spatial light modulator 30 is provided as one forwhich a desired phase pattern φ_(desire) and a distortion correctionpattern φ_(correction) are superimposed on this blazed grating patternφ_(grating). However, a phase pattern φ_(phase) being a sum of thedesired phase pattern φ_(desire) and the distortion correction patternφ_(correction) is applied with phase folding, and has a phase modulationrange of 2π or less. This phase pattern φ_(result) is presented in thespatial light modulator 30. The phase modulation range in this phasepattern φ_(result) is 4π or less.

In the present embodiment, since a phase pattern φ_(result) produced bysuperimposing a blazed grating pattern φ_(grating) for light diffractionwith a phase modulation range of 2π or less and a phase patternφ_(phase) having a predetermined phase modulation distribution with aphase modulation range of 2π or less is presented in the spatial lightmodulator 30 with a phase modulation range of 4π, a light after beamshaping having a desired intensity distribution and phase distributioncan be obtained, without the necessity for performing phase folding forthe phase pattern φ_(result). On the other hand, in the comparativeexample, since a spatial light modulator with a phase modulation rangeof 2π is used, a phase pattern after phase folding is displayed in thatspatial light modulator, and therefore, a light after beam shapinghaving a desired intensity distribution and phase distribution cannot beobtained.

By thus performing beam shaping by the light control device 1 accordingto the present embodiment, an input light where the intensitydistribution in a beam section is non-uniform can be converted to anoutput light where the intensity distribution in a beam section is asdesired. For example, beam light with a Gaussian distribution can beshaped into beam light with a uniform distribution called a flat-topbeam. Such a beam shaping technique is useful for processingapplications, illumination for a microscope, and the like.

INDUSTRIAL APPLICABILITY

The present invention provides a light control device capable ofobtaining light having a desired beam section in the technique ofcausing a phase modulating spatial light modulator to present a phasepattern produced by superimposing a blazed grating pattern and a phasepattern having a predetermined phase modulation distribution.

The invention claimed is:
 1. A light control device comprising: a lightsource that outputs light; a phase modulating spatial light modulatorthat is capable of phase modulation in each of a plurality oftwo-dimensionally arrayed pixels in a range of 4π, is input with lightoutput from the light source, presents a phase pattern to modulate thephase of light in each of the pixels, and outputs light after beingphase-modulated by this phase pattern; and a control unit that causesthe spatial light modulator to present a phase pattern produced bysuperimposing a blazed grating pattern for light diffraction with aphase modulation range of 2π or less and a phase pattern having apredetermined phase modulation distribution with a phase modulationrange of 2π or less, and adjusts the light diffraction efficiency in thespatial light modulator by adjusting the blazed grating pattern, whereinthe phase modulation range of the phase pattern produced bysuperimposing the blazed grating pattern and the phase pattern having apredetermined phase modulation distribution is 2π or more; and phasefolding is not performed for the phase pattern produced by superimposingthe blazed grating pattern and the phase pattern having a predeterminedphase modulation distribution.
 2. The light control device according toclaim 1, wherein the control unit causes the spatial light modulator topresent a phase pattern for which the blazed grating pattern having alight diffraction efficiency distribution according to an intensitydistribution in a beam section of a Laguerre-Gaussian mode beam with aspecific index and the phase pattern having a phase modulationdistribution according to a phase distribution in a beam section of theLaguerre-Gaussian mode beam are superimposed.
 3. The light controldevice according to claim 1, wherein the control unit causes the spatiallight modulator to present a phase pattern for which the blazed gratingpattern having a light diffraction efficiency distribution according toan intensity distribution of light having a specific intensitydistribution and phase distribution in a beam section and the phasepattern having a phase modulation distribution according to the phasedistribution are superimposed.
 4. A light control method using: a lightsource that outputs light; and a phase modulating spatial lightmodulator that is capable of phase modulation in each of a plurality oftwo-dimensionally arrayed pixels in a range of 4π, is input with lightoutput from the light source, presents a phase pattern to modulate thephase of light in each of the pixels, and outputs light after beingphase-modulated by this phase pattern, a control unit for causing thespatial light modulator to present a phase pattern produced bysuperimposing a blazed grating pattern for light diffraction with aphase modulation range of 2π or less and a phase pattern having apredetermined phase modulation distribution with a phase modulationrange of 2π or less, and adjusting the light diffraction efficiency inthe spatial light modulator by adjusting the blazed grating pattern,wherein the phase modulation range of the phase pattern produced bysuperimposing the blazed grating pattern and the phase pattern having apredetermined phase modulation distribution is 2π or more; and phasefolding is not performed for the phase pattern produced by superimposingthe blazed grating pattern and the phase pattern having a predeterminedphase modulation distribution.
 5. The light control method according toclaim 4, for causing the spatial light modulator to present a phasepattern for which the blazed grating pattern having a light diffractionefficiency distribution according to an intensity distribution in a beamsection of a Laguerre-Gaussian mode beam with a specific index and thephase pattern having a phase modulation distribution according to aphase distribution in a beam section of the Laguerre-Gaussian mode beamare superimposed.
 6. The light control method according to claim 4, forcausing the spatial light modulator to present a phase pattern for whichthe blazed grating pattern having a light diffraction efficiencydistribution according to an intensity distribution of light having aspecific intensity distribution and phase distribution in a beam sectionand the phase pattern having a phase modulation distribution accordingto the phase distribution are superimposed.